Preclinical evaluation of N4-beta-D-ribofuranosyltriazin-3-one-N1,-oxide, uricytin, which is a powerful inhibitor of murine leukemia L1210, P388 and adenocarcinoma 755, is proposed. The drug is effective against 6MP and Ara C resistant strain of L1210 leukemia and is cytotoxic to both proliferating and nonproliferating cells. The studies proposed for this period will investigate acute and chronic toxicities of uricytin in laboratory rodents and drug distribution, disposition and metabolism in experimental animal tumor models. Further investigation of drug mechanism of action will be performed in order to provide a rational chemotherapeutic back up for subsequent clinical trials. BIBLIOGRAPHIC REFERENCE: N4-beta-D-Ribofuranosyltriazin-3-one-N1-oxide (uricytin), a New Nucleoside Analog Exhibiting Broad Spectrum Antitumor Activity, Tasneem A. Khwaja, Linda Kigwana and Roland K. Robins, Abstract C-60, 9th International Congress Chemotherapy 1975, London.